Combined fire alarm,burglar alarm,and intercommunication system



Dec. '30. 1969 J c. MIDKIFF 3,487,404

COMBINED FIRE ALARM, BURGLAR ALARM, AND INTERCOMMUNICATION SYSTEM FiledMarch 23, 1967 INVENTOR. JAMES C. M IDKIFF ATTORNEY United States PatentU.S. Cl. 340-416 3 Claims ABSTRACT OF THE DISCLOSURE A latchingmultivibrator provides an audio tone of a given frequency when a firesensor, associated with that multivibrator, is activated. A secondlatching multivibrator provides a tone of another frequency when aburglar sensor, associated with the second multivibrator, is activated.The output of the second-mentioned multivibrator is utilized to modulatethe output of the firstmentioned multivibrator when a burglary issensed, the second multivibrator being then utilized to start the first.The inventive combination includes a rotary action control switch whichhas four positions, a first position for permitting a response either tofire or burglary, a second position for off or resetting functions, athird position for permitting a response to fire only, and a fourthposition in which the operation of the first-mentioned multivibrator istested.

BACKGROUND OF THE INVENTION The present invention provides controlcircuitry which, when used in conjunction with an intercommunicationsystem having a sound channel, provides means for detecting suchundesired hazards as burglary or fire, and adds these additionalfunctions to the normal function of an intercornmunication system.

The prior art includes many arrangements for providing an audio tone inresponse to the Sensing of a fire and coupling that audio tone into theloud speakers of an intercornmunication system. Such a system is shown,for example in United States patent to Wooten, No. 2,942,245.

The present invention provides an arrangement which furnishes an alarmin the event of either burglary or fire. In the system of the presentinvention there is a relatively small number of components. The presentinvention uses solid state active elements and latching multivibrators,which assure that an alarm, once rendered, will continue to be givenuntil a human operator intervenes and resets the system.

The present invention further includes a rotary switch device operativeto provide the functions mentioned in the abstract set forth above.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention,together with other and further objects, advantages and capabilitiesthereof, reference is made to the following description of theaccompanying drawings, in which:

FIG. 1 is a circuit schematic of a combined burglar and fire alarmcircuit in accordance with the present invention; and

FIG. 2 is a circuit schematic of a representative one of the twolatching multivibrators incorporated in the system.

DETAILED DESCRIPTION OF THE INVENTION The thesis of the invention isthat upon actuation, sensors such as 21 and 22 for burglary and 57 and58 3,487,404 Patented Dec. 30, 1969 for fire, drive a radiointercornmunication system into rapid continuous alarm, with on-offtones characteristic of either burglary or fire. Once triggered, thealarm operates indefinitely until to control switch is turned to a resetposition.

Detection of burlary is achieved by the use of switch sensors, normallyclosed, located at doors and windows, such as the elements designated bythe reference numerals 21 and 22. Burglary alarm sensors are per se wellknown in the art and are normally closed switches which are mechanicallyor electrically opened by a disturbance caused by a burglary.

Detection of fire is achieved through the use of normally closed thermalswitches located at strategic environmental positions throughout thebuilding or home containing the switches. Fire sensors are also per sewell known to those in the art and are essentially thermally operatedswitches which automatically open at an elevated temperature such as F.,for example. See 57 and 58.

The control circuitry in accordance with the present invention is soarranged that the burglary alarm has a distinctly different tone thanthe fire alarm. By reason of this the home owner can distinguish thetype of hazard to which he is alerted and can initiate appropriateprotective action.

The invention can operate equally well with any type ofintercornmunication system having an audio channel and speaker system,such, for example, as an intercommunication system including a built-inradio receiver or one including an audio amplifier of some kind. Ineither event the output of the system herein disclosed is applied to anaudio amplifier for the purpose of providing audible signals.

In accordance wtih the invetnion the audible alarm for the indication offire consists of a 1000 cycle audio tone while the audible alarmindicating the presence of a burglar consists of that tone, modulated ata lower frequency, that is to say, a wavering audible tone.

The invention utilizes latching multivibrators. Once triggered, an alarmis maintained even though the sensing circuit is restored to normal.

Referring now specifically to FIG. 1 of the drawings, there will be seena 5 cycle latching multivibrator comprising transistors 10 and 14 and a1000 cycle latching multivibrator comprising transistors 52 and 34,together with a rotary switch 27. The burglar sensors 21 and 22 areconnected in series between ground and the junction of resistors 16 and18. The fire sensors 57 and 58 are connected in series between point 40and contact 43 of the switch, which is grounded during normal operation.As shown in FIG. 1, the system will respond to a momentary opening ofeither of the two sensor circuits in order to provide an audible alarm.

When either of the burglar sensors 21 and 22 is open, the multivibratorcomprising transistors 10 and 14 will start and remain on. The output ofthe multivibrator is coupled through capacitor 24 and diode 25 to aresistor 48, to produce a pulsating positive voltage across resistor 48which is applied to the bases of transistors 52 and 34. This voltagestarts the multivibrator comprising the transistors 52 and 34 andmodulates its frequency at a 5 cycle rate. If one of the fire sensors 57or 58 only is activated, the 1000 cycle multivibrator comprisingtransistors 52 and 34 alone will start and will remain on. Thismultivibrator cannot start the five cycle multivibrator because of thepresence of diodes 25 and 26. That is, in response to a sensing of fire,the 1000 cycle multivibrator furnishes an off-on tone. In response tothe sensing of the presence of a burglar, this 1000 cycle tone ismodulated at 5 cycles by the 5 cycle multivibrator, so that a waveringtone is produced. t

NPN transistor has an emitter connected to ground 11 and a collector incircuit, via resistor 12, with the positive terminal 13 of the powersupply. NPN transistor 14 has an emitter connected to ground 11 and acollector connected to terminal 13 via resistance 15. It will be seenthat both collectors are biased in the nonconductive direction. The basebias network for transistor 10 comprises resistors 16 and 17 and thebase bias network for transistor 14 comprises resistors 18 and 17,resistor 17 being connected between terminal 13 and the junction ofresistors 16 and 18. A capacitor 19 is connected between the collectorof transistor 14 and the base of transistor 10 and capacitor 20 isconnected between the collector of transistor 10 and the base oftransistor 14.

In the ready state of this circuit transistors 10 and 14 are cut off andcapacitors 19 and 20 are charged to the full power supply voltage ofplus 10 volts. The junction of resistors 16, 17 and 18 is held at groundpotential by reason of the sensing switches 21 and 22, which areconnected in series between point 23 and grounded conductor 11.

When any one of the burglary sensing switches 21, 22 is open, then apositive potential is available at point 23 and the bases of bothtransistors are positively biased relative to ground so that the circuitof transistors 10, 14 then operates as a conventional multivibratorproducing a square wave output at the collector of transistor 14 whichis applied across resistor 48 via coupling capacitor 24.

Even when the opened sensing switch 21 or 22, as the case may be, isclosed, grounding point 23, the multivibrator will continue to operate,in what is called a latching state. That is, the multivibratorcomprising 10 and 14. Let it be assumed that transistor 10 has justchanged from a conducting to a cut-off state, whereupon capacitor 20begins to charge through the emitter to base circuit of transistor 14and resistor 12. Transistor 14 will be saturated until capacitor 20 isalmost completely charged and capacitor 19 will discharge throughresistors 16 and 18 and produce a reverse bias to cut off transistor 10as transistor 14 is saturated. After capacitor 20 is charged transistor14 will no longer be saturated and capacitor 19 will now begin to chargethrough the emitter to base circuit of transistor 10 and resistor 15.Transistor 10 will now be saturated and transistor 14 will be cut off byreason of the discharge of capacitor 20 through resistors 16 and 18.After capacitor 19 has completely charged, transistor 10 will cut oiland this cycle will continue until the reset switch 27, which is closedto connect the base of transistor 10 to ground 11, is actually closed,connecting 39 and 38.

The 1000 cycle multivibrator comprises the following circuit elements,each element referred to in the following table being generally similarto that opposite it in the five cycle multivibrator column, as tabulatedbelow.

5 cycle multivibrator: 1000 cycle multivibrator 17 4s, 49 12 50 51 10 5216 53 18 54 14 34 55 19 56 junction of resistors 53 and 54. A capacitor56 is connected between the collector of transistor 34 and the base oftransistor 52 and capacitor 55 is connected between the collector oftransistor 52 and the base of transistor 34.

In the ready state of this circuit transistors 52 and 34 are cut off andcapacitors 56 and 55 are charged to the full power supply voltage ofplus 10 volts. The junction of resistors 48 and 49 is held at groundpotential by reason of the sensing switches 57 and 58, which areconnected in series between point 40 and conductor 42, grounded via 43,44, 45 and 11.

When any one of the fire sensing switches 57 or 58 is open, then apositive potential is available at point 40 and the bases of bothtransistors 52 and 34 are positively biased relative to ground so thatthe circuit then operates as a conventional multivibrator producing asquare wave output at the collector of transistor 34 which is applied toan audio amplifier (not shown).

' Even when the opened sensing switch 57 or 58, as the case may be, isclosed, grounding point 40, the multivibrator including transistor 52and 34 will continue to operate, in what is called a latching state. Letit be assumed that transistor 52 has just changed from a conducting to acut-off state, whereupon capacitor 55 begins to charge through theemitter to base circuit of transistor 34 and resistor 50. Transistor 34will be saturated until capacitor 55 is almost completely charged andcapacitor 56 will discharge through resistors 53 and 54 and produce areverse bias to cut off transistor 52 as long as transistor 34 issaturated. After capacitor 55 is charged transistor 34 will no longer besaturated and capacitor 56 will now begin to charge through the emitterto base circuit of transistor 52 and resistor 51. Transistor 52 will nowbe saturated and transistor 34 will be cut olf by reason of thedischarge of capacitor 55 through resistors 53 and 54. After capacitor56 has completely charged, transistor 52 will cut off and this cyclewill continue until the switch contacts 36, 37, 38 which are closed toconnect the base of transistor 34 to ground 11, are actually closed.

In the switch position shown in FIG. 1 the fire sensor switch circuit isclosed between junction point 40 and ground by conductor 41, conductor42 and contacts 43, 44 and 45. This position is the normal operatingposition in which circuitry responds either to the sensing of a fire orthe sensing of an unlawful entry by a burglar.

In the first position counterclockwise to that shown the base oftransistor 34 is grounded via conductor 35, contact 36, contact 37 andcontact 38, and the base of transistor 10 is grounded via contact 39,contact 37 and contact 38. This is the off or reset position of switch27.

In the fire only (two steps counterclockwise) position of the switch 27the base of transistor 10 is grounded via conductor 46 and contacts 39and 38 and the base of transistor :14 is grounded via contacts 47, 37and 38. This is the fire only position.

In the fire test position (three steps counterclockwise) the fire sensorcircuit will open because conductor 42 cannot be grounded.

The series diode 25, in series between capacitor 24 and resistor 48, ispoled to pass positive voltages to resistor 48 and the shunt diode 26 ispoled not to short out such voltages. However, these diodes preventsignal outputs from the 1000 multivibrator from starting the 5 cyclemultivibrator;

It will be understood that the output terminal marked 30 in FIG. 1 andthe grounded line 1-1 constitute signal output terminals that providethe audio tones hereinabove described. These outputs are applied to theinput of any conventional sound channel system that includes an audioamplifier. The postulate of this discussion is that the audio amplifier(not shown) is suitably ready for operation or capable ofbeing'triggered into operation by the presence of the audio signalsproduced by the FIG. 1 circuit. Audio amplifying systems and radiocommunication systems are per se well known to those skilled in the artand therefore are not described herein.

I claim:

1. A system for furnishing to an existing sound communications channelcharacteristic signals indicative of the presence of either a burglaryhazard or a fire hazard comprising in combination:

signal generating means in the form of a first latching multivibratorfor producing a characteristic signal capable of being modulated,modulating means in the form of a second latching multivibrator forproducing a modulating signal,

first sensing means responsive to one of said hazards for initiatingoperation of the signal generating means to produce said characteristicsignal in unmodulated form, and

second sensing means responsive to the other hazard for initiatingoperation of the modulating means, the modulating means being coupled tothe signal generating means so that the modulating means starts thesignal generating means and modulates the signal which it produces, saidsignal generating means being adapted to be coupled to saidcommunications channel,

means for so biasing each of said multivibrators that it continuesoperation until disabled, and

switching means for disabling said multivibrators.

2. A system for furnishing to an existing sound communications channelcharacteristic signals indicative of the presence of either a burglaryhazard or a fire hazard comprising in combination:

a source of current having positive and negative signals,

signal generating means for producing a characteristic signal capable ofbeing modulated,

modulating means for producing a modulating signal,

each of the modulating means and the signal generating means comprisinga first transistor having an emitter and collector and base, loadresistors for the collectors, capacitors intercoupling the base of eachtransistor with the collector of the other, and a T- shaped resistancenetwork providing a junction and having its ends connected to saidpositive terminal and said bases,

fire sensing means responsive to a fire hazard for initiating operationof the signal generating means to produce said characteristic signal inunmodulated form, and

burglary sensing means responsive to the burglary hazard for initiatingoperation of the modulating means, the modulating means being coupled tothe signal generating means so that the modulating means starts thesignal generating means and modulates the signal which it produces, saidsignal generating means being adapted to be coupled to saidcommunications channel, and

means for encircuiting the burglary sensing means with the modulatingmeans comprising a series connection of the burglary sensing meansbetween said junction and ground,

the fire sensing means being adapted to be connected.

between ground and a potential point between the positive terminal andthe junction of the T-shaped resistance network associated with thesignal generating means.

3. The combination in accordance with claim 2 and a switch having fourpositions and contacts adapted to make circuits as follows:

in the first position, to connect the fire sensing means between groundand said point,

in the four position, to disconnect the fire sensors transistorassociated with the modulating means and the second transistorassociated with the signal generating means,

in the third position, to ground the bases of both transistors of themodulating means, and

in the fourth position, to disconnect the first sensors from ground.

References Cited UNITED STATES PATENTS 3,051,944 8/1962 Smith. 3,137,8466/1964 Keeling. 3,174,143 3/1965 Akin 340276 JOHN W. CALDWELL, PrimaryExaminer PERRY PALAN, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,487,404 December 30 1969 James C. Midkiff It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 2, line 4, "to", first occurrence, should read a line 34"invetnion" should read invention Column 3 line 40 "long as" should beinserted at the beginning of the line; line 71 "inthe" should read inthe Column 6 Claim 3 should appear as shown below:

3. The combination in accordance with Claim 2 and a switch having fourpositions and contacts adapted to make circuits as follows in the firstposition, to connect the fire sensing means between ground and saidpoint in the second position, to ground the bases of the firsttransistor associated with the modulating means and the secondtransistor associated with the signal generating means in the thirdposition, to ground the bases of both transistors of the modulatingmeans and in the fourth position, to disconnect the fire sensors fromground.

Signed and sealed this 9th day of June 1970 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

